This invention relates generally to methods for beneficiation of kaolins and other clays, and more specifically relates to a method for improving the brightness of kaolin clays by removal of titaniferous discolorants therefrom.
Natural clays, including kaolin clays, frequently include discoloring contaminants in the form of iron and/or titanium-based impurities. Quantities of titanium-based impurities are particularly significant in the case of the sedimentary kaolins of Georgia, where such impurities are commonly present as iron stained anatase and rutile. In order, therefore, to refine the clay and bring the brightness characteristics of the resultant product to a level acceptable for such applications as paper coating, various techniques have been used in the past to remove such discoloring impurities. Thus, for example, hydrosulfites have been widely used for converting at least part of the iron-based (or "ferruginous") impurities to soluble forms, which may then be removed from the clay.
Among the most effective methods for removing titaniferous impurities, including e.g. iron stained anatase, are the well-known froth flotation techniques. According to such methods, an aqueous suspension or slurry of the clay is formed, the pH of the slurry is raised to an alkaline value, for example, by addition of ammonium hydroxide, and a collector agent is added. The slurry is then conditioned by agitating same for a relatively sustained period. A frothing agent, for example, pine oil, is added to the conditioned slurry, after which air is passed through the slurry in a froth flotation cell, to effect separation of the impurities along with the collector agent.
Further details regarding the use of froth flotation techniques for removing titanium-based impurities from kaolins, may be found at numerous points in the prior art, including, for example, in U.S. Pat. No. 3,450,257 to E. K. Cundy. The Cundy disclosure will be found illustrative further, of the fact that the prior art has almost universally regarded fatty acids, most notably oleic acid, as the collector agents appropriate and effective for use where titanium-based impurities are to be removed.
Within more recent years it has been reported that certain classes of phosphate esters can serve as collector agents in mineral beneficiation processes. Thus, for example, U.S. Pat. No. 3,480,143 to Mitzmager et al, teaches that certain acid esters of phosphorous acids are useful in flotation separation of a siliceous ore into a floated heavy mineral fraction, and a non-floated siliceous fraction. Of perhaps more pertinence to the present invention are the disclosures of Yang, U.S. Pat. Nos. 3,804,243 and 3,837,488, wherein complex phosphate esters of the type considered in the present invention are reported as useful in flotation processes for separating mica and kaolin clays in a crude ore containing both components.